QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1037 40V MICROPOWER DFN BUCK REGULATOR WITH INTEGRATED BOOST AND CATCH DIODES LT3470 DESCRIPTION Demonstration circuit 1037 is a 40V micropower DFN buck regulator featuring the LT(R)3470. The board is optimized for 5V output at up to 200mA load current for a steady state input voltage range of 5.5V to 40V. With its wide input voltage range, high efficiency internal power switch, low dropout operation, hysteretic current-mode, integrated boost and catch diodes and tiny SOT-23 package, the LT3470 is a very versatile and powerful IC for DC/DC converters that require extremely compact space, high efficiency and high input voltage. The LT3470 hysteretic control scheme allows all of the components to be small, surface mount devices while providing minimum output ripple voltage at all load currents. The current-mode control topology creates fast transient response and good loop stability with a minimum number of external components. The low resistance internal power switch achieves high efficiencies of up to 82% at 12V input. The shutdown jumper can be used to place the part in micropower shutdown, reducing supply current to less than 1A by driving the pin low. The internal boost and catch diodes simplify layout and reduce component count, providing the smallest solution possible. The LT3470 datasheet gives a complete description of the part, operation and applications information. The datasheet must be read in conjunction with this Quick Start Guide for demonstration circuit 1037. In particular, the datasheet section on `Thermal Calculations' is important for estimating whether a given application's combination of input voltage, load current, ambient temperature and frequency will cause the LT3470 to exceed it's absolute maximum rated junction temperature. The LT3470EDDB is assembled in a small low profile DFN package. Proper board layout is essential for maximum thermal performance. See the datasheet section `Layout Considerations'. Design files for this circuit board are available. Call the LTC factory. LT is a trademark of Linear Technology Corporation QUICK START PROCEDURE Demonstration circuit 1037 is easy to set up to evaluate the performance of the LT3470. Refer to Figure 1 for proper measurement equipment setup and follow the procedure below: NOTE: Make sure that the input voltage does not ex- ceed 40V. NOTE: The shutdown jumper shunt is required to be placed in the shutdown position or the VOUT ENABLE position for proper operation. NOTE: Do not hot-plug the input voltage terminal VIN. The absolute maximum voltage on VIN is 40V and hot-plugging a power supply through wire leads to the demonstration circuit can cause the voltage on the extremely low-ESR ceramic input capacitor to ring to twice its DC value. In order to protect the IC, a higher ESR Aluminum Electrolytic capacitor is placed at the input terminals. This may protect against some, but not all, input transients due to hot-plugging with a power supply. See Application Note 88 for more details. NOTE: Connect the power supply (with power off), load, and meters as shown in Figure 1. 1. After all connections are made, turn on input power and verify that the output voltage is 5V. 1 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1037 40V MICROPOWER DFN BUCK REGULATOR WITH INTEGRATED BOOST AND CATCH DIODES NOTE: If the output voltage is too low, temporarily disconnect the load to make sure that the load is not set too high. serve the output voltage regulation, ripple voltage, efficiency and other parameters. 2. Once the proper output voltages are established, adjust the load within the operating range and ob- Figure 1. Proper Measurement Equipment Setup 2 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1037 40V MICROPOWER DFN BUCK REGULATOR WITH INTEGRATED BOOST AND CATCH DIODES 3